Multi-spectral light source systems are particularly useful in color image projection devices and systems. One commonly known multi-spectral light source is a reflective light system, which is shown in FIG. 1. This system includes an intense white light source LS produced, for example by an arc lamp. The white light generated by the light source LS can be decomposed into three primary color components, in this case red green and blue light. The first optical element struck by the white light is a dichroic filter RR. Dichroic filters are used in the art for reflecting a desired color of light and passing all other colors of light. The filter RR is placed at about a 45 degree angle so as to reflect the red component of the white light by 90 degrees through a series of additional optical elements. The first one of these elements is a conventional mirror M1 that changes the direction of the red light by about 90 degrees. The red light is then shaped by an optical slit element denoted by the numeral S1 that creates a bar of red light. This bar of red light then passes through a rotating prism P1 so as to cause the red bar of light to scroll across a light valve LV. The scrolling action can progress in many orientations across the light valve e.g. horizontally, vertically or diagonally, but is usually scrolled vertically from top to bottom. Prior to reaching the light valve LV, the scrolling bar of red light passes through two other dichroic filters RG2 and RB that respectively reflect only green and blue light. The scrolling red bar of light then passes through an image block IB and onto the reflective light valve LV. The light valve LV modulates the red light bar with red pixel information to form the red portion of an image which is then reflected back to a screen S. The screen S then reflects the red portion of the image to the observer.
The green component of the white light passes through the filter RR and is reflected via a dichroic filter RG1 that reflects only green light and allows the blue light to pass. The green light, which has now changed direction by 90 degrees, passes through a second optical slit element S2 and a second rotating prism P2. The second slit S2 and prism P2 form a scrolling bar of green light in manner similar to the red bar. The scrolling bar of green light is then reflected by the dichroic filter RG2 to join the green scrolling bar with the red scrolling bar. The two bars do not overlap and maintain their relative position on the light valve via coordinated controls in the rotating prisms P1 and P2. The green bar then passes through the dichroic filter RB to the image block IB and onto the reflective light valve LV. The light valve LV modulates the green light with green pixel information to form the green portion of the image, which is then reflected back to the screen S. The screen S then reflects the green portion of the image to the observer.
The blue component of the white light passes through the filters RR and RG1 where it is shaped by a third optical slit element S3 into a bar of blue light. This bar of light is then scrolled via a third prism P3 in a manner similar to the red and green light. The bar of blue light then reflects off a second conventional mirror M2 and the dichroic filter RB to the image block IB and onto the reflective light valve LV. The light valve LV modulates the blue light with blue pixel information to form the blue portion of the image which is then reflected back to the screen S. The screen S then reflects the blue portion of the image to the observer. More specifically, the scrolling bar of blue light is coordinated with the green and red light so that none of the bars overlap and the entire light valve is illuminated. As the different bars of light progress across the light valve LV, different pixel information is used to modulate the different light colors so that an integrated color image appears to the observer.
FIG. 2 shows another type of commonly known multi-spectral light source, referred to as a transmissive light system. The transmissive light system generates colored light bars in a manner that is substantially identical to the reflective light system described in FIG. 1, except, the light valve LV′ modulates light as it passes through to the screen S, which reflects the image to an observer.
Another commonly known multi-spectral light source is a flashing lamp system. Flashing lamp systems employ a static color division system comprised of a lamp for each of the primary colors: red, green, and blue. A color image is provided by sequentially flashing the lamps coordinated with related color information on a light valve (either reflective or transmissive).
These multi-spectral light source systems have some disadvantages. In reflective light systems, the prisms used for spectrally dividing the white light generated by the light source increases the cost, size and power requirements of the system. Flashing lamp systems are also expensive because of the use of multiple lamps with their associated reflectors and lens systems. Since the light generating portions of these systems serve only to create three scrolling or flashing bars of light for illuminating the light valve, a light generating system that can produce scrolling or flashing bars of light while providing reduced space, cost and power requirements would be desirable.